1. Field of the Invention
This invention relates to an apparatus and method for machining the annular seats of gate valves, and in particular, to such an apparatus and method which utilizes the gate guide rails inside the valve chamber for fixturing.
2. Background of Information
A gate valve has two confronting annular seats and a gate which slides on a pair of guides cast or welded on opposite sides of a valve chamber midway between the seats. The gate is operated manually or by an actuator between an open position and a closed position in which disks on the gate seat against the two annular valve seats. The annular valve seats and the gate disks are tilted at the same small angle from the axis through the valve to facilitate seating of the disks against the valve seats.
There are many applications where gate vanes are used. One such application is in nuclear power plants. Many such valves in nuclear power plants have satellite hard facing material on the valve seats. The satellite contains cobalt which becomes activated by the radioactive coolant which passes through the valves. Removing the satellite hard facing in situ has been a difficult and time consuming process which exposes workers to radiation. Current practice has been to cut out the valves and remove them to other facilities where the satellite hard facing is removed and replaced by a stainless steel overlay. The stainless steel overlay is laid down by a weld which must then be machined.
Removal of the gate valve from the piping system for refurbishing is expensive and time consuming. There is a need, therefore, for apparatus which can machine seats of gate valves without removing the valves from the installation.
There is a further need for such apparatus which requires minimum operator presence to reduce radiation exposure.